Image processing system and method employing a threaded scheduler

ABSTRACT

A system and method are disclosed for an image processing system including a threaded scheduler providing compact and efficient dataflow as a pipeline management and data flow layer.

This application claims priority from U.S. Provisional Application 60/752,423 for an “Image Processing System and Method Employing a Threaded Scheduler,” by P. Emmett et al., filed Dec. 21, 2005, which is also hereby incorporated by reference in its entirety.

A methodology is disclosed for an image processing system, and more particularly, a threaded scheduler providing compact and efficient dataflow as a pipeline management and data flow layer for use with an image processing platform.

BACKGROUND AND SUMMARY

U.S. Pat. No. 6,286,026, for a “Method and Apparatus for Integrating Pull and Push Tasks in Pipeline Data Processing,” by D. L. Venable et al. (Sep. 4, 2001), hereby incorporated by reference in its entirety, teaches a device and method for processing data with a data processing string having push type and pull type tasks.

In a chunk-based image processing pipeline there needs to be a system to process each chunk of data by each processing step in an efficient manner. This system needs to control the flow of the chunks as well as the order of execution of the processing steps.

A threaded scheduler, as disclosed herein, breaks up an image processing pipeline into a collection of traces, which are a sequence of processing steps or “engines”. This collection of traces is processed by one or more threads as each trace's “engines” bercome scheduled for execution. At the execution of each “engine”, data chunks are taken from upstream “engines” and processed by the “engine”. Resulting data chunks are then passed to downstream “engines”. This taking/passing of chunks may schedule or block the execution of additional “engines” based on the arrival of data or the triggering of limits on links between “engines.”

The Engines platform provides many powerful image processing operations in a very modular and dataflow neutral system. Although the dataflow neutral aspect is powerful, by providing integration with various dataflows, it poses a problem if one doesn't have a dataflow. The disclosed system and method fills this void by providing a compact and efficient dataflow for use with the Engines platform.

One of the disclosed embodiments processes data in chunks and supports any type of data that Engine does, including such types as compressed data. It also supports the efficient buffer management of Engines by allowing chunks to migrate down a pipeline, reducing the need for copies and re-buffering of data. The disclosed embodiments can handle simple linear pipelines to more complex pipelines, described with Directed Acyclic Graphs or DAGs, with multiple branches and joins. In accordance with the embodiment, a DAG my be made dynamically or on the fly using calls to add nodes and lines or the DAG may be saved and loaded using an extensible markup language (XML) based description. The embodiment disclosed below also supports the concept of DAGs within DAGs, by providing the ability to encapsulate a sub-DAG within a node of a larger DAG. This powerful feature allows for “code reuse” at the DAG level by having a useful DAG reused in a larger operation.

Disclosed in embodiments herein is a method for processing image data, comprising: defining a multi-trace directed acyclic graph, including breaking a directed acyclic graph for processing image data into a plurality of traces, wherein each trace is a fragment of the directed acyclic graph; and executing the multi-trace directed acyclic graph wherein each trace is executed in a separate thread.

Also disclosed in embodiments herein is a system for processing image data in a networked computing environment, comprising: an image data source; a host system, connected to said image data source via the network, wherein said host system includes an image processing pipeline, said pipeline operating on chunks of image data from said source; and memory for storing said chunks of image data during and upon completion of the data by the pipeline.

Disclosed in a further embodiment herein is an image processing pipeline, comprising: a client layer; an dataflow layer, said dataflow layer including at least one interface and service to describe, run, and feed the image-processing pipeline; and an Engine layer, wherein said dataflow layer controls the operation of at least one node in said Engine layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a general illustration of a directed acyclic graph in accordance with an aspect of the disclosed system and method;

FIG. 2 is an partial illustration of a network architecture in an embodiment of the systems and methods disclosed herein;

FIG. 3 is a simple flow diagram illustrating a processing pipeline in accordance with embodiments of the systems and methods disclosed herein;

FIGS. 4A and 4B illustrate examples of the manner in which the dataflow scheduler manages traces and any associated chunks of image data;

FIGS. 5 and 6 are state diagrams illustrating the general operation of the scheduling and mapping operations for the disclosed system and method; and

FIG. 7 is an exemplary representation of a flow diagram illustrating stages of a buffer mapping operation in accordance with the disclosed system and method.

DETAILED DESCRIPTION

As used herein the term “DFlow” is employed to characterize a pipeline management and data flow layer for use with Engines. Prior to the creation of DFlow, the responsibility for connecting multiple Engines together fell to the client. With DFlow, any client may easily construct and execute Engine based image processing pipelines. The acronym DAG refers to a Directed Acyclic Graph, which is generally a graph of nodes linked together, typically where no output from one node is feed back into the node, directly or indirectly. The term “pipeline” refers to an executable DAG of Engines. A “scheduler” is an object capable of selecting tasks from a list and performing them in a reasonable order. A “chunk” is a portion of a data stream. A chunk may contain all or some of an entire stream object, and in accordance with an embodiment disclosed herein, a chunk contains an integral number of image scanlines. An Engine chunk (XEngChunk) is a structure that contains a description of a particular buffer and its contents. A “trace,” given an ordered set of tasks that may branch and join (a DAG), is one possible way to traverse the task list such that all tasks are given an opportunity to run before any task is repeated. A trace may be built with an execution order in which a source runs first, then the Engine using the output of the source, then a third Engine using the output of the second, etc. A single trace may represent an entire DAG or multiple traces may be created to divide the DAG into pieces. Each trace may be executed simultaneously and asynchronously in different threads.

As set forth above the system and method disclosed herein can handle simple linear pipelines to more complex pipelines, often referred to as DAGs, including DAGS with multiple branches and joins and those with DAGs within DAGs. In one embodiment, the methods described herein may be implemented in computer software (code) and may be used to operate a computer system such as a Linux, Windows, Solaris or a Mac OSX computer platform suitable for running Engines or the like.

An example of a DAG 100 is depicted in FIG. 1, where a series of nodes 110 are employed to represent various operations. Referring also to FIG. 2, at a more detailed level the system provides a monolithic dataflow layer 210 for Engines because the dataflow logic, and code, is not spread across individual processing nodes. Instead, the nodes do not talk to each other but to a single instance of the scheduler 220. Also included within the dataflow layer 210 are a DAG Manager 250 and a Buffer manager 270. DAG Manager 250 allows the client to describe the nodes and edges of a DAG, where the nodes represent the Engines and the edges represent the data flow links between them. The Buffer Manager 270 is responsible for handling the chunk buffers: migratable, non-migratable, and client-owned.

The scheduler 220 is responsible for dividing the DAG into executable traces and then creating threads to run the traces, and therefore has the job of communicating with the nodes 110, moving data between them and determining when an Engine should be executed to process more data. In essence the scheduler 220 moves down the list of nodes, executing them when they have work to do and moving the resulting chunks (not shown) to other nodes based on where the links 230 point. This approach, of having the dataflow in one object, matches well with the modular nature of Engines.

The dataflow layer 210 provides a data flow package that resides between the client (208) and the Engine (212) layers. It contains all the necessary interfaces and services to describe, run, and feed an image-processing pipeline.

A client could use the dataflow layer 210 in a variety of ways, but there are some consistent steps. Every client must start by creating a new instance of the object and end by deleting that instance. An instance of the object may be reused any number of times before it is ultimately deleted.

One example of a client could be a DAG Editor. This type of client would use a DAG Manager API to create a DAG description and then have save the description to an XML file to be used later. Another example of a client could be a pipeline server 310 as generally illustrated by the operations depicted in FIG. 3. The pipeline server would receive an XML 320 file from a remote user, load the XML 330 into an instance, run the pipeline 340, and return the results 350 to the remote user. The system and method disclosed herein contemplate a client used by Engine and pipeline developers that would have many of these features combined. Such a system would allow the developer to edit the DAG, run the pipeline, perform pipeline debugging, and collect performance statistics.

While the disclosed system and method can execute a DAG as a complete unit, the disclosed systems and methods further contemplate a more powerful execution option—breaking a DAG 100 up into traces 120. Each trace is merely a fragment of the complete DAG 100. With a multi-trace DAG each trace is executed in a separate thread. This single DAG then has the ability to utilize more then one processor in a multi-processor system. It may also be useful on a single processor system where an Engine is waiting on a task to complete, such as an outside piece of hardware, disk, network, coprocessor, etc., and the host processor could be doing more work elsewhere on the DAG.

Currently there are two ways to fragment a DAG into traces. One is automatic and the other is manual. In the automatic embodiment, a new trace is created for each source Engine finds (readjpg, pattern, etc.), and then grows that trace by following the links out from that Engine. The manual embodiment requires the DAG developer to set a “threadbreak” on selected links (e.g., 230) in the DAG. This “threadbreak” will cause the DAG to fragment, and form a new trace, at this link.

Using the present system and method, it is possible to leverage the broad image processing available with Engines, providing an efficient and easy to use dataflow. With direct support for Engines, the full features of Engines can be exploited, without the need to handle the complex aspects of the dataflow.

In accordance with an embodiment of the present system and method, the threaded scheduler 220 breaks up an image processing pipeline into a collection of traces, which are a sequence of processing steps or “engines.” A trace is started at each source “engine” and continues to the downstream “engines” until no remaining “engines” are available. “Engines” that already belong to a trace or are past a thread break are not added and followed. Generally, a thread break is a user settable hint on the pipeline that indicates a desired break point.

Referring next to FIGS. 4A and 4B, which depict functionality of the dataflow scheduler 220, the collection (waiting list 440) of traces 410 is processed by one or more threads 420 as each trace's “engines” become scheduled for execution by the scheduler. At most, there are as many threads as there are traces. The threads efficiently wait on the traces to be scheduled for execution. When a trace being waited on is scheduled for execution, counter 450 (nReady) is incremented. The counter indicates how many Engines are ready to execute. Subsequently, a thread awakens and takes the trace. The thread processes the trace's “engine” 460 sequence in order until the end and places the trace back into the waiting list 440. The thread then returns to waiting on the trace list.

At the execution of each “engine”, data chunks 476 are taken from upstream “engines”. All output queues 480 that are below a user settable level are provided with an empty chunk, the others are “plugged” with a zero sized chunk to prevent output. These chunks are then processed by the “engine” 460. Resulting data chunks are subsequently passed to downstream “engines” 460. Any unprocessed input chunks 476 are returned to their respective input queue 480 (see also waiting list 440 in FIG. 4A). If this “engine” consumed or produced any chunks then it is scheduled for execution. If the removal of the upstream chunk caused the output queue of the upstream “engine” to go below a user settable level then that “engine” will be scheduled for execution by marking its trace ready and adjusting the nReady counter accordingly. If the passing of the downstream chunk caused new data to arrive at the downstream “engine” then that “engine” will be scheduled for execution

To increase the efficiency of the chunk passing, the chunks are owned by the scheduler and can migrate down the pipeline without being copied. This also allows the chunks to queue up where necessary with no additional copying. If a chunk gets branched and sent to one or more “engines” it will be marked read only and sent along with its reference count increased accordingly. The scheduler tracks the references to the chunks and frees and/or reuses the chunks when needed.

Having described the general operation of the dataflow scheduler and several examples of functionality of a system or method employing the various elements described, attention is now turned to providing more detail relative to an embodiment of the system and method. As described herein, various aspects are implemented in an object oriented design in ANSI C to match the existing Engine design and language constraints.

The system and method give the client layer the ability to describe an image processing pipeline, save that description in memory (RAM, magnetic media, etc.), load a previously saved description from memory, run the currently loaded description, and extract performance statistics. The client may choose to run a pipeline using one of the following methods:

-   Non-interactive: Describe, Run, Wait for completion. This would be     typical for a pipeline server that is handed a complete DAG and     asked to execute it to completion. -   Interactive build: Run, Describe and test at each step, wait for     completion.

This method might be used by a client for a DAG that would change its shape depending on the type of image to be processed. For instance, an Engine that splits an image into its component channels doesn't know how many outputs it will have until it sees the actual image to be split. It could be RGB (3), CMYK (4), or have any number of additional tag channels (n).

-   Chunked stream: Describe/Run, then Feed and Retrieve chunks     interactively as indicated above relative to FIG. 4. A client that     receives the input image as a chunked stream (like a web server) may     wish to begin processing and return output without having to buffer     the entire image. This is particularly important when running on a     limited memory system where the size of a single frame buffer may     exceed the total available RAM.

The client may also choose to run the directed acyclic graph in one of three threading modes:

-   Client Thread: The client must call the DFlow_Process method to     allow the DAG to execute. This would be necessary for an interactive     pipeline debugger as well as on a platform that does not support     threading. -   Limited Threads: The Scheduler will create up to a specified number     of threads and run the DAG with those threads. This would be     appropriate on a system with limited computing resources where the     client wishes to prevent DFlow from monopolizing the CPU. This might     also be a good idea for a pipeline server where many instances of     DFlow may need to share the system resources. -   Unlimited Threads: The Scheduler will create as many threads as     needed to have at least one thread per trace. This would be the     normal mode of operation for a system requiring maximum performance.     However, it is important to note that a DAG is most efficient with a     few, well-selected traces.

There are several major classes employed in a system as described herein. The primary object is referred to as DFlow. A single DFlow can host a single DAG. If a client desires to have multiple concurrent DAGs, it may create multiple instances of DFlow. A DFlow object contains the collection of Engine instances, the links between them, and a scheduler object for running them. The methods of DFlow define the client API. They allow the client to create and edit a DAG description, run the pipeline, and retrieve performance and success statistics. Another class is XFEng, which represents a node in the pipeline graph. An XFEng contains the details of the node's name and parameters. Once the pipeline is running, it also holds the actual Engine instance, performance statistics, and buffer management structures. XFLink is an edge in the pipeline graph. An XFLink contains buffers that are in transition between Engines and in some cases between scheduler threads. XFBuf represents a buffer holding stream data. An XFBuf contains an XEngChunk along with enough information to chain XFBufs into a list and free them when they're done. An XFBuf may hold a chunk allocated by the DFlow layer, by an Engine, or by the client. The XFBufMgr is an XFBuf allocator class. An XFBufMgr can create XFBuf objects, free them and other tracking details. An example of the XBUf instance is the buffer manager 270 of FIG. 2. The XFScheduler represents a class responsible for creating XFThreads for executing XFTraces. Threads are controlled based on the maxThreads value set by the client and the actual number of traces. Lastly, XFParams are a class responsible for managing parameter sets and translating parameter templates into actual parameter lists. A client that creates or loads a pipeline description containing macros (a parameter template) must also provide a macro substitution list at runtime.

DFlow is the top-level object and presents the client API. DFlow has many public methods, but no public data members. To enforce this restriction in ANSI C, DFlow is implemented as an opaque structure. The following table (Table A) characterizes the DFlow Data members: TABLE A Type Name Description unsigned version The DFlow version number. This value is filled with the constant, DFLOW_VERSION when the object is constructed and used to validate the object on later calls through the API. HXFLock lock The DFlow state lock is used to protect the global state. XFState state The current state of the DFlow object: Idle, Run, Pause, Complete, Error. XFList <HXFEng> Engines The collection of XFEng objects that comprise the current DAG. XFList <HXFLink> links The collection of XFLink objects that connect the Engines in the current DAG. XEngCriticalSection csDag A lock for the DAG tree items. HXFEng root The top(root) engine in the DAG tree. unsigned engineUID A UID for new engines. HXFBufMgr bufMgr The Buffer Manager. XEngCriticalSection csEvents The lock for the events list and trigger. XFList statusEvents The collection of XEngEvent objects to trigger on status change. unsigned wdTimeout The watchdog timeout amount in milliseconds. XFBool wdTriggered The status of the watchdog timer. XEngCriticalSection csErrorMsg The lock for the error message. XTSTR errorMessage Common and useful messages recorded here. XFPerfCallbacks cbacks The performance monitoring callback functions. XFScheduler scheduler An embedded XFScheduler object.

Furthermore, the following tables provide further characterization of the DFlow structure: Table B characterizes the DFlow methods and objects, Table C characterizes the DAG Manager functionality; Table D characterizes the characterizes the Pipeline Runner function; Table E characterizes the Port Interface. TABLE B Return Type Name Parameters Description XFResult DFlow_Init void Create a new reference to the DFlow package. This will initialize any internal structures and dependencies. DFlow_Cleanup must be called once for each time that DFlow_Init is called. XFResult DFlow_Cleanup void Remove a reference to the DFlow package. If the last reference is removed, the internal structures are cleaned up. This function will fail if there are any outstanding DFlow object instances. DFlow_Cleanup must be called once for each call to DFlow_Init. XFResult DFlow_New HDFlow Create a new DFlow object instance. *pDFlow void DFlow_Delete HDFlow Destroy an existing DFlow object instance. DFlow

TABLE C Return Type Name Parameters Description XFResult DFlow_DAGEmpty HDFlow dflow Discard the current DAG description. XFResult DFlow_DAGLoad HDFlow dflow Load a new DAG description from an XEngIO *io XML representation. An XEngIO object is used to abstract the I/O source. Any existing DAG description is discarded. (For details on XEngIO, please refer to the Engine API docs.) XFResult DFlow_DAGSave HDFlow dflow Save the current DAG description to a XEngIO *io serialized representation. An XEngIO object is used to abstract the I/O destination. XFResult DFlow_DAGAddXEng HDFlow dflow Adds an Engine to the DAG. XCTSTR iName must be a unique name for this iName instance of the Engine. If iName is XCTSTR NULL, then a unique name will be mName generated automatically. const mName is the name of the Engine type XFParams of which to create an instance. *params params specifies the parameter set to void *clientData be stored in the DAG. clientData is a HXFEng pointer to a client private data block. *Instance This may be NULL. unsigned instance may hold a reference to an linkCount XFEng. If non-NULL, a handle to the . . . new XFEng will be returned. This handle may then be used for other operations. linkCount indicates the number of input links to create along with the instance. “is the variable arg list of input links specified as: H XFEng srcInst, unsigned srcIx pairs. The order of the pairs maps to the order of the input chunks on the new instance. XFResult DFlow_DAGAddXEngEx HDFlow dflow Adds an Engine to the DAG as a child HXFEng parent node to another XFEng node. XCTSTR The function works like iName DFlow_DAGAddXEng with addition of XCTSTR the parent field and the flags field. mName The flags is a bitwise or'd field. If const XF_ENG_AUTOFORMAT is used then XFParams the Engine will have autoformat before *params it in the pipeline. unsigned flags When child nodes are added to a void *clientData parent node they act as a sub-DAG HXFEng under the parent node. The child nodes *instance can be linked together and to the input unsigned and outputs of the parent. A NULL linkCount parent is valid and is the same as using . . . DFlow_DAGAddXEng. XFResult DFlow_DAGDeleteXEng HDFlow dflow Deletes an Engine instance. Any links HXFEng attached to the instance are also instance deleted. XFResult DFlow_DAGAddLink HDFlow dflow Creates a new link from the output of HXFEng srcInst one XFEng instance to the input of unsigned another. If the new link conflicts with srcChunkIx any existing link, the original link is HXFEng removed. destInst The two XFEng nodes must be siblings unsigned (have the same parent) or one must be destChunkIx the parent of the other. The same node unsigned may be used as both the source and wantsDataThreshold destination, it will cause the input of the XFBool node to be directly wired to the output. threadBreak A NULL node may be used, it represents the top (root) node of the DAG. The inputs and outputs of the top node are the ports of the DAG and can be driven using the Port Interface functions. srcInst and srcChunkIx specify the instance and output chunk index of the source Engine. destInst and destChunkIx specify the instance and input chunk index of the destination Engine. wantsDataThreshold indicates the throttle threshold on this link. XF_MAX_DEPTH specifies that the queue is not throttled. (See XFLink for more details.) threadBreak is a hint to the scheduler that the downstream XEng should be in a different thread than the upstream XEng. A thread break will only be created if threading is actually enabled. XFResult DFlow_DAGDeleteLink HDFlow dflow Deletes a link by specifying either the HXFEng source or the destination point of the instance link. If the referenced point is an input, unsigned then just the one link is deleted. If the chunkIx point is an output, then all links from XFBool input that point are deleted. HXFEng DFlow_DAGGetXEngInst HDFlow dflow Locates and returns the Engine XCTSTR instance with the specified name. iName Returns NULL if the name is not found. HXFEng DFlow_DAGGetXEngInstEx HDFlow dflow Locates and returns the child Engine HXFEng instance with the specified name. instance Returns NULL if the name is not found. XCTSTR iName XFResult DFlow_DAGGetFuncDesc HDFlow dflow Fills a preallocated XEngFuncDesc with XEngFuncDesc the formal arguments of the current *funcDesc pipeline. The argument list is generated by scanning the Engine parameters for macros and compiling the results. The resulting XEngFuncDesc may be passed directly to XEngCmdLnToArgv for converting command line parameters into a parameter substitution list suitable for passing to DFlow_PipeRun. XFResult DFlow_DAGRename HDFlow dflow Renames the XFEng instance specified HXFEng by the provided handle to a new name. instance This replaces the unique ID string with XCTSTR a new one that must conform to all the newName unique ID string rules. XFResult DFlow_DAGSetParams HDFlow dflow Replaces the current parameter set HXFEng with a new one. instance const XFParams *params XFResult DFlow_DAGSetClientData HDFlow dflow Store the pointer to a client data block HXFEng in the specified Engine instance. instance void *clientData XFResult DFlow_DAGGetClientData HDFlow dflow Retrieve the pointer to the client data HXFEng block from the specified Engine instance instance. void **clientData XFResult DFlow_DAGGetXEngInfo HDFlow dflow Fills a client-supplied XFEngineInfo HXFEng struct with information about the instance specified XFEng instance. XFEngineInfo *info XFResult DFlow_DAGGetXEngPerfStats HDFlow dflow Fills a client-supplied XFPerfStats HXFEng struct with performance statistics about instance the specified XFEng instance. XFPerfStats *stats XFResult DFlow_DAGSetStateEventCallback HDFlow dflow Sets the state event callback function. HXFStateEvent The supplied function will be called Func pFunc each time an XEng in the DAG void * changes state. clientData Set pFunc to NULL to disable callbacks. XFResult DFlow_DAGSetDataEventCallback HDFlow dflow Sets the data event callback function. HXFDataEvent The supplied function will be called Func pFunc each time an XEng in the DAG receives void *clientData or sends a block of data. Set pFunc to NULL to disable callbacks. XFResult DFlow_DAGSetInputName HDFlow dflow Sets the name for an input of an XFEng HXFEng instance. instance unsigned idx XCTSTR name XFResult DFlow_DAGSetOutputName HDFlow dflow Sets the name for an output of an HXFEng XFEng instance. instance unsigned idx XCTSTR name XFResult DFlow_DAGFindInput HDFlow dflow Finds the input of an XFEng instance HXFEng with the name given. instance unsigned *idx XCTSTR name XFResult DFlow_DAGFindOutput HDFlow dflow Finds the output of an XFEng instance HXFEng with the name given. instance unsigned *idx XCTSTR name

TABLE D Return Type Name Parameters Description XFResult DFlow_PipeRun HDFlow dflow Places the Pipeline into the Run state. unsigned No Engines will actually be initialized maxThreads during this call. The client may specify char the maximum allowable scheduler *paramsList[ ] threads and a parameter substitution XCTSTR list at this time. logBase If maxThreads is set to XF_UNLIMITED_THREADS, then the scheduler will create as many threads as there are traces. paramsList references the parameter substitution list. logBase is the base pathname for generating performance logfiles for this run. If logBase is NULL, then performance logging is suppressed. XFResult DFlow_PipeWaitForInit HDFlow dflow Waits for a specific XFEng instance to HXFEng complete initialization. If no XFEng is instance specified, waits for the entire pipeline to unsigned initialize. The client may provide a timeout timeout. DFlow_PipeProcess will be called internally in the client thread mode. XFResult DFlow_PipeProcess HDFlow dflow Allows the scheduler to run when XFBool DFlow is in the client thread mode. The singleStep scheduler will run either one or all Engines in the pipeline before returning, depending on the singleStep flag. This function returns immediately in either the limited or unlimited thread modes. XFResult DFlow_PipePause HDFlow dflow Stops the scheduler but retains the pipeline state. This can be useful for inspecting the pipeline for errors or other status. Call DFlow_PipeContinue to continue processing. This call will return XF_FAIL if DFlow is not in the Run state. XFResult DFlow_PipeContinue HDFlow dflow Restarts the scheduler from the Pause state. This call will return XF_FAIL if DFlow is not in the Pause state. XFResult DFlow_PipeWaitForComplete HDFlow dflow Allows the client to go into an efficient unsigned wait state until the entire pipeline timeout completes processing or an error or XFBool timeout occurs. *allComplete The completion or error status of the XFBool pipeline is returned in allComplete and *errorDetected errorDetected. DFlow_PipeProcess will be called internally when in client thread mode. XFResult DFlow_PipeWaitFor HDFlow dflow Allows the client to go into an efficient unsigned wait state until the entire pipeline timeout completes processing or an error or unsigned timeout or watchdog timeout occurs. *pStatus The resulting status is returned in the pStatus. DFlow_PipeProcess will be called internally when in client thread mode. XFResult DFlow_PipeCleanup HDFlow dflow Releases all scheduler and pipeline state information. DFlow returns to the Idle state. XFResult DFlow_PipeAllComplete HDFlow dflow Queries the pipeline to see if all XFBool Engines have completed without any *allComplete errors. XFResult DFlow_PipeAllRunning HDFlow dflow Queries the pipeline to see if all the XFBool Engines are still running. This implies *pAllRunning none are complete and there are no errors. XFResult DFlow_PipeErrorDetected HDFlow dflow Queries the pipeline to see if any XFBool Engines have posted an error. *pErrorDetected XFResult DFlow_PipeGetStatus HDFlow dflow Queries the pipeline and state flags for unsigned the current status. *pStatus XFResult DFlow_PipeAddEvent HDFlow dflow Adds an event to the dispatch list. This XEngEvent event will be triggered when a status *event change occurs. XFResult DFlow_PipeRemoveEvent HDFlow dflow Removes an event from the dispatch XEngEvent list. *event XFResult DFlow_PipeSetWDTimeout HDFlow dflow Sets the watchdog timeout in unsigned milliseconds. The default is 60 timeout seconds. If no work is performed within this timeout the watchdog is triggered. XFResult DFlow_PipeResetWD HDFlow dflow Resets the state of watchdog timeout. XFResult DFlow_PipeGetErrorMsg HDFlow dflow Queries the pipeline to see if any XTSTR *msg Engines have posted an error message.

TABLE E Return Type Name Parameters Description XFResult DFlow_PortGetInputCount HDFlow dflow Queries the pipeline to see how many unsigned input ports are available. This *count information is also returned with DFlow_DAGGetFuncDesc. XFResult DFlow_PortSendHeader HDFlow dflow Sends a header into an input port. The unsigned idx header is duplicated to aid tracking and XEng HeaderStruct ownership issues. *hdr XFResult DFlow_PortSend HDFlow dflow Sends a chunk into an input port. The unsigned idx chunk is duplicated to aid tracking and XEngChunk ownership issues. *chunk XFResult DFlow_PortGetInputStatus HDFlow dflow Gets the status of an input port. unsigned idx unsigned *status XFResult DFlow_PortSetInputEvent HDFlow dflow Sets the status event of an input port. unsigned idx This event is triggered when the port XEngEvent status changes. *event XFResult DFlow_PortSetInputError HDFlow dflow Marks an input port as having an error. unsigned idx XFResult DFlow_PortGetOutputCount HDFlow dflow Queries the pipeline to see how many unsigned output ports are available. This *count information is also returned with DFlow_DAGGetFuncDesc. XFResult DFlow_PortRecvHeader HDFlow dflow Recieves a header from an output port. unsigned idx The header is duplicated to aid tracking XEngHeaderStruct and ownership issues. This call does **hdr not block, it is an error if the header is not ready. XFResult DFlow_PortRecv HDFlow dflow Recieves a chunk from an output port. unsigned idx The chunk is duplicated to aid tracking XEngChunk and ownership issues. This call does *chunk not block, it is an error if a chunk is not ready. The chunk parameter can be NULL which just discards the next available chunk. XFResult DFlow_PortPeek HDFlow dflow Returns a reference to a chunk from an unsigned idx output port. The chunk is not duplicated XEngChunk nor is it removed from the output. The *chunk chunk should be removed with DFlow_PortRecv when the next chunk is needed. This call does not block, it is an error if a chunk is not ready. XFResult DFlow_PortGetOutputStatus HDFlow dflow Gets the status of an output port. unsigned idx unsigned *status XFResult DFlow_PortSetOutputEvent HDFlow dflow Sets the status event of an output port. unsigned idx This event is triggered when the port XEngEvent status changes. *event XFResult DFlow_PortSetOutputError HDFlow dflow Marks an output port as having an unsigned idx error.

Having described the DFlow object in general, the Detailed Dynamic Model will now be set forth and described with reference to FIG. 5. The DFlow object has five states: Idle (510), Run (520), Pause (530), Complete (540), and Error (550). DFlow is initialized to the Idle state 510, and may be moved to the Run state 520 at any time by calling the DFlow_PipeRun method. DFlow will not return to the Idle state until DFlow_PipeCleanup is called.

When in the Run state 520, DFlow will create new scheduler traces and start running. All sources will be initialized along with the Engines they feed. Data will begin flowing down the pipeline. The data flow will block if it reaches an unconnected output. The client may add new Engines to unconnected outputs at any time, thus allowing the dynamic construction of a pipeline. The client may not remove or alter an individual Engine once it has been initialized since the stream cannot be “rewound” and reprocessed with a new Engine. New sources may, however, be added at any time while in the Run state.

From the Run state 520, DFlow may move to Idle 510, Pause 530, Complete 540, or Error 550. DFlow_PipeCleanup will cause a return to Idle. DFlow_PipePause will set the Pause state. The completion of all Engines will set the Complete state 540. The error of any Engine will set the Error state 550. DFlow will remain in Pause until the client calls DFlow_PipeRun to continue processing or DFlow_PipeCleanup to return to the Idle state 510. DAG changes in the Pause state 530 have the same restrictions as in the Run state 520. Lastly, DFlow will remain in Complete 540, or Error 550 until DFlow_PipeCleanup is called. This allows the client to review the pipeline state if desired. (e.g. for a post-mortem.) All DAG changes are prohibited in the Complete and Error states, 540 and 550, respectively.

From the functional perspective, when an Engine instance is added using the DFlow_DAGAddXEng method, it is placed in an instance array. If any links are specified as arguments on this call, they are added to the Link array and connected from the outputs of the specified Engine instance(s) to the inputs of the new Engine. When Links are added using the DFlow_DAGAddLink method, they are placed in the Link array. They are also connected to their respective source and destination Engine instances.

As mentioned in the dynamic model described above, new Engines and links may be added to unconnected outputs of the DAG even when DFlow is in the Run state 520. If this occurs, the dataflow scheduler must regenerate its traces before continuing. Also, recall that an Engine or Link may not be removed once it has been initialized; DFlow_PipeCleanup must be called first.

One problem with dynamically building a pipeline arises when adding a branch to a partially initialized pipeline. Imagine a source feeding a single Engine (not a Sink). When run, the source and Engine will initialize and begin processing the stream. A portion of the stream will move out of the source and into the Engine where it will block due to the unconnected output. In this state, an attempt to add a new Engine that connects to the source (as a tee-branch) will fail because a portion of the stream has already moved out of the source and cannot be repeated.

Having described the dynamic and functional aspects of DFlow, attention is directed to the following information, which is related to the XFEng detailed design. Generally, an XFEng object represents an Engine in the DAG, hosts the Engine instance, and handles its execution state and data flow control.

In the following detailed object model: Table F characterizes the XFEng Data Members; and Table G characterizes the XFEng Methods. TABLE F Type Name Description unsigned valid Magic number that identifies a valid XFEng object. This field is set to XFLOW_ENGINE when the object is constructed and used to validate the instance when its methods are called. HXFLock lock Lock for the instance. XTSTR iName Unique instance name: readint1, invert1, etc. XTSTR mName Engine type name: readint, invert, etc. XFParams params The parameter or template set. unsigned flags Engine flags, currently only autoformat. void * clientData The pointer to the client's private data block. XEngFuncDesc *desc The function description (containing the argument list and init point) for the associated Engine. This value is set during XFEng_New if the xeng library is available. Otherwise it is left as NULL until it is time to init the Engine. XFEngState state The current position of this instance in the execution state machine. XFBool hadData This flag indicates that the last call to Process returned output data. XFBool usedData This flag indicates that the last call to Process used input data. XFBool canContinue This flag indicates that the last call to Process returned the status XENG_CAN_CONTINUE and thus wishes to be called again, even in the absence of new input data (or output space). XEngState * xeState The pointer to the Engine state. This value is NULL before the Engine Init function is called. XFArray input The array of XFInput handlers. This array maps <HXFInput> directly to the input chunks on the Engine. XFArray output The array of XFOutput handlers. This array maps <HXFOutput> directly to the output chunks on the Engine. XFPerfStats perf The struct containing the performance statistics for this instance. HXFEng afhandle Reference to autoformat Engine. HXFEng ophandle Reference to the actual Engine in autoformat mode. HXFEng parent Reference to parent Engine, NULL for root node. XFList children List of child Engines: <HXFEng> <HXFEng> HDFlow dflow Reference to DFlow instance. HXFScheduler scheduler Reference to the scheduler. Will be NULL when DFlow is in the Idle state. XEngEvent * traceEvent Reference to the trace event.

TABLE G Return Type Name Parameters Description XFResult XFEng_New HDFlow dflow Creates and initializes a new HXFEng parent XFEng. Node will be placed under XCTSTR iName parent node, which may be XCTSTR NULL. mName See DFlow_DAGAddXEng for const XFParams details on iName, mName, flags *params and params. unsigned flags HXFEng *pxEng void XFEng_Delete HXFEng xeng Cleans up and deletes an XFEng instance. XFResult XFEng_SetInputLink HXFEng xeng Sets the input link for the unsigned specified chunkIx to be link. The chunkIx previous link on that chunk, if any, HXFLink link is returned in pOldLink. HXFLink *pOldLink XFResult XFEng_AddOutputLink HXFEng xeng Adds link as a new output branch unsigned to the specified chunkIx. chunkIx Returns XF_FAIL if xeng has HXFLink link already produced data on this output. XFResult XFEng_RemoveOutputLink HXFEng xeng Removes link from the list of unsigned outputs on the specified chunkIx. chunkIx Returns XF_FAIL if link was not HXFLink link attached to the output or if xeng has been initialized. XFResult XFEng_RemoveAllOutputLinks HXFEng xeng Removes all the links from the unsigned specified chunkIx. The list of chunkIx links that were formerly attached XFArray *pLinks are copied into the client-provided XFArray pointed to by pLinks. Returns XF_FAIL if xeng has been initialized. XFResult XFEng_Rename HXFEng xeng Renames xeng to be iName. XCTSTR iName XFResult XFEng_SetParams HXFEng xeng Sets a new parameter set for const XFParams xeng. *params XFResult XFEng_GetInfo HXFEng xeng Fills the client-provided XFEngineInfo XFEngineInfo structure. All fields *pInfo are shallow copies and must not be freed by the caller. XFResult XFEng_GetPerfStats HXFEng xeng Fills the client-provided XFPerfStats XFPerfStats structure. *pStats XFResult XFEng_Start HXFEng xeng Move the XFEng from the Idle HXFScheduler state to the Tolnit state. scheduler This method returns XF_FAIL if the XFEng is not in the Idle state. XFResult XFEng_Schedule XFEng xeng Informs this node that it has been HXFScheduler scheduled and the trace event is. scheduler XEngEvent *traceEvent XFBool XFEng_IsStarted HXFEng xeng Queries the XFEng to see if it has been started. XFBool XFEng_IsScheduled HXFEng xeng Queries the XFEng to see if it has already been scheduled. XFBool XFEng_IsComplete HXFEng xeng Queries the XFEng to see if it is complete. A node is complete once all child nodes are complete and EODs have passed all inputs and outputs. XFResult XFEng_SignalTraceEvent HXFEng xeng Sets the trace event. This may trigger this nodes trace to be run. XFResult XFEng_Process HXFEng xeng Runs the XFEng through one const cycle of its state machine. What XFParamMap happens depends on the state *paramMap and the available buffers. See 6.2.3 for details. Idle, Complete, Error: Do nothing. ToInit: Collect input headers and then call the Engine Init point. The contents of paramMap are used to resolve any parameter macros. No Valid Outputs: Collect input data and then call the Engine Process point. Running: Collect input data and output buffers, call the Engine Process point, and reconcile the status of all buffers. XFResult XFEng_Cleanup HXFEng xeng Performs the steps necessary to call the Engine end point until the Engine is destroyed and then dispose of any held buffers. This function may be called at any time to return to the Idle state.

As will be appreciated, the XFEngine employs various internal classes and operations. The XFEngineInfo class (Table H) is filled from information in the XFEng instance. The XFPerfStats class (Table I) is stored within the XFEng class and copied out on request from the client. Table J illustrates the XFStats in accordance with an embodiment of the system described herein. TABLE H Type Name Description XCTSTR iName The unique instance name. XCTSTR mName The Engine type name. XFParams * pParams The parameter or template set. XFEngState state The current state of the XFEng. XEngState xeState A copy of the public portion of the Engine state structure.

TABLE I Type Name Description unsigned nInputs The number of input ports. XFStats input[ ] The statistics blocks for the input side. The size of this array is set by the XF_MAX_PORT_STATS constant. unsigned nOutputs The number of output ports XFStats output[ ] The statistics blocks for the output side. The size of this array is set by the XF_MAX_PORT_STATS constant. XEngInt64 init The number of ticks charged to initialization. XEngInt64 work The number of ticks charged to process calls that produced results. XEngInt64 overhead The number of ticks charged to the management overhead.

TABLE J Type Name Description unsigned buffers The total number of buffers filled/consumed unsigned bytes The number of bytes processed. unsigned tBytes The total number of bytes expected on this port. This will be set to zero if the total byte count is not known at the start of processing and for non-image types. unsigned scanlines The number of scanlines processed. unsigned tScans The total number of scanlines expected on this port. This will be set to zero for non-image types. unsigned pixels The number of pixels processed.

The XFInput and XFOutput classes, Table K and Table L, respectively, are use to handle the mapping of Engine input and output ports into DFlow. In one embodiment there is exactly one XFInput or XFOutput instance for each input or output chunk on the Engine, although it may be conceivable that alternative arrangements may be useful. Each instance of XFInput holds a reference to an XFLink, a private header copy, an event to use instead of the trace event and a port name. Each instance of XFOutput holds a reference to an XFLink, a reference to the output header, an event to use instead of the trace event, a busy chunk and a port name. TABLE K Type Name Description HXFLink link The link that supplied the buffer. XEngHeaderStruct* hdr Our own input header, must be freed. XEngEvent* event Link event, if not NULL use instead of trace event. XTSTR name A port name.

TABLE L Type Name Description HXFLink link The downstream link. XEngHeaderStruct* hdr Reference to the header for this output. XEngEvent* event Link event, if not NULL use instead of trace event. HXFBuf busyChunk The busy Engine owned buffer. XTSTR name A port name.

In the detailed dynamic model, for example as depicted in FIG. 6, the XFEng class has six states. The edges shown are for normal operation. It is also possible to return to Idle from any state by calling Cleanup. The states are as follow:

-   -   Idle (610)—The initial state on creation. This is the state         before Start and after Cleanup.     -   To Init (620)—The initial state after Start. The instance is         ready to be initialized when all of its input headers are         available. After initialization, the state will move to No Valid         Outputs, Running, or Error as appropriate.     -   No Valid Outputs (640)—The instance has successfully         initialized, but has set the “XENG_OUTPUTS_NOT_VALID_SFLAG”         flag. It can accept input, but will not produce any output. It         will stay in this state until it clears the flag or signals an         error.     -   Running (660)—The instance has successfully initialized and         cleared the “XENG_OUTPUTS_NOT_VALID_SFLAG” flag. The         availability of output headers is determined by the         “XENG_OUTPUT_NOT_VALID_OFLAG” flag on each output port. The         instance can accept input and may produce output. It will stay         in this state until it completes or flags an error.     -   Complete (650)—The instance has consumed the entire input stream         and produced an entire output stream. Its process point shall         not be called again, but its end point has not been called yet.         It will remain in this state until Cleanup is called.     -   Error (630)—The instance has produced an error. Its process         point shall not be called again, but its end point has not been         called yet. It will remain in this state until Cleanup is         called.

An XFEng, in the functional model, is responsible for hosting an Engine instance and managing its state and data flow. To do this, it provides methods to start, run, and cleanup the Engine. To manage the data flow for an Engine, an XFEng must handle the inbound and outbound motion of XFBufs. XFBufs as described below. When the XFEng_Start method is called and the XFEng is in the Idle state 610, it is moved to the Tolnit state 620. Otherwise, the method returns XF_FAIL.

When the XFEng_Cleanup method is called, the XFEng is cleaned up and returned to the Idle state 610. When the XFEng_Process method is called, the behavior depends on the current state. The Idle 610, Complete 650, and Error 630 states will return immediately. The other states will proceed as depicted, for example, in FIG. 7.

Referring to FIG. 7, several stages represent complex activities. The details of those steps are expanded in the following description. In the “Have Required Buffers?” stage 710, the system analyzes the input and output arrays. If there is no pending input, the Engine did not do any work on its last Process call, and the Engine is not a Source, so it is skipped. If not skipping, and the Engine supports migratable buffers, then migratable buffers are allocated for each output that is not throttled (all downstream links do not want any more data). If an output is throttled, then allocate a NULL migratable buffer. If not skipping and the Engine does not support migratable buffers, then skip the Engine if any busy flags are set or any output is throttled.

Relative to the “Move and/or Free Buffers” stage 720, an XEngChunk is a buffer descriptor that resides on each input and output “port” of an Engine. As a buffer passes through a port, the description of that buffer is copied into or out of the relevant XEngChunk. Since the descriptor is owned by the Engine, it cannot travel with the buffer. To allow buffer migration, and to track non-migratable buffers, DFlow creates an XFBuf wrapper for each buffer. During the call to the Process point 712, a reference to the XFBuf is stored in the XEngChunk's User Data field.

After the Process call 712 returns, the inputs and outputs are scanned for buffers that need to be moved and/or freed. Depending on the XENG_MIGRATE_SFLAG, buffer chunks left on inputs may be released. In non-migrate mode, XFBuf_Done is called unless the buffer has been passed through to an output. In migrate mode, the XENG_FINISHED_CHUNK flag indicates that a buffer should be released, otherwise it is left alone.

Non-NULL buffer chunks left on outputs are moved to the output XFLink(s). If an output has multiple branches, then the buffer chunk must be duplicated and distributed appropriately. A further optimization may be implemented when a buffer is marked with the Read Only flag. These buffers may be shared on the downstream branches using a reference counting mechanism.

The held queue is scanned for buffers with their XENG_FINISHED_CHUNK flag set. Any buffers with the flag set are released.

Lastly, at various points, the XFEng needs to pass headers from the Engine's output to the downstream links where they may be read by the next Engine(s) in the pipeline. The actual header is not copied during this process, only a reference is copied.

In one embodiment of the disclosed system and method, an XFLink is the connection between two XFEng instances. The XFLink also contains a thread-safe FIFO (to hold any buffers passing down the pipeline) and references to the source and destination XFEng instances. Given that each XFEng is responsible for getting and putting buffers from/to its links, the source and destination references are used primarily for allowing a link to cleanly remove itself from the pipeline and also to help serialize the links to external storage. The following are more descriptive characterizations of aspects of the XFLink functionality: Table M is a characterization of the XFLink data members; Table N is a characterization of the XFLink methods; and Table O suggests that XFLink contains the XFLinkEnd class. TABLE M Type Name Description XEngCriticalSection* cs The mutex for this link. XFList<HXFBuf> queue The list of XFBufs currently queued on this link. XFBufs will be added to the queue at the tail and removed at the head. unsigned wantsDataThreshold The threshold at which this link will vote to apply backpressure. If all the links connected to a single output unanimously vote for backpressure, then the output is throttled. Default is 1. XFBool threadBreak A flag to indicate that the downstream Engine should be executed in a different thread from the upstream one if multithreading is enabled. Default is false. XEngHeaderStruct* hdr A reference to the XEngHeader that applies to the data flowing through this link. XFLinkEnd src The XFEng and chunk index for the Engine producing buffers for this link. XFLinkEnd dst The XFEng and chunk index for the Engine consuming buffers from this link.

TABLE N Return Type Name Parameters Description XFResult XFLink_New unsigned Creates and initializes a new wantsDataThreshold XFLink. XFBool threadBreak If wantsDataThreshold is set HXFEng src to XF_MAX_DEPTH, the link unsigned srclx will request up to UINT_MAX HXFEng dst buffers. This disables all unsigned dstlx backpressure on this link. HXFLink *pLink void XFLink_Delete HXFLink link Removes this link from the DAG and cleans up the references to it in the source/dest XFEng instances. XFResult XFLink_PutBuf HXFLink link Adds a buffer to the queue. HXFBuf buf XFResult XFLink_TakeBuf HXFLink link Removes a buffer from the HXFBuf *pBuf queue. XFBool XFLink_IsEmpty HXFLink link Returns an XFBool indicating that the queue is empty. XFBool XFLink_WantsData HXFLink link Returns an XFBool indicating that the link wants more buffers. XFBool XFLink_IsFull HXFLink link Returns an XFBool indicating that the queue is full.

TABLE O Type Name Description HXFEng instance Reference to the XFEng instance to which this link is connected. unsigned chunklx Index of the connected chunk on that XFEng.

In the dynamic model of XFLink, when the FIFO contains no XFBufs, XFLink_IsEmpty will return XF_TRUE. When the FIFO contains fewer than wantsDataThreshold XFBufs, XFLink_WantsData will return XF_TRUE, and when there are XF_MAX_DEPTH XFBufs in the FIFO, XFLink_IsFull will return XF_TRUE.

Functionally, XFLink is intended to act as an intermediary between two XFEng instances, either in the same or in independent threads. Each call to query or modify the queue state is protected by a mutex. The PutBuf method will append a new Buf to the tail of the queue. The call will return XF_FAIL if the queue is already full. If the queue is going from empty to non-empty, the downstream Engine is signaled ready to run. The TakeBuf method will remove a Buf from the head of the queue. The call will return XF_FAIL if the queue is already empty. If the queue is going from not wanting to wanting data, the upstream Engine is signaled ready to run.

Considering the XFBuf functionality referred to above, attention is now turned to the detailed design of the XFBuf. An XFBuf is an XEngChunk descriptor with the added ability to be linked into lists and to be returned to a buffer manager. Since an Engine buffer is just a block of memory with no associated descriptor, an XFBuf is created to describe the buffer and travel with it between Engines. An XFBuf is created by an XFBufMgr. The following tables set forth the detailed object model for the XFBuf: Table P characterizes the XFBuf Data Members; and Table Q characterizes the XFBuf Methods.

The XFBuf class does not have any states or state transition events, and an XFBuf is created and owned by an XFBufMgr (see below). The XFBuf is passed around amongst the XFEng instances until it is not needed any more. At that time, the last XFEng will call XFBuf_Done and return the buffer to its owner. TABLE P Type Name Description XEngChunk chunk An instance of the XEngChunk structure. This is used to carry the chunk values from one Engine to the next and preserve them when the buffer is queued. unsigned alignment The alignment of the data block in this buffer. HXFBufMgr bmObj The handle to the XFBufMgr that created this buffer. This is used to free the buffer. void* bmData The XFBufMgr private data. unsigned refs The reference count to this XFBuf.

TABLE Q Return Type Name Parameters Description XFResult XFBuf_NewRef HXFBuf buf Creates a new reference to the XFBuf. HXFBuf This will set the XFBuf to be ReadOnly *newRef and increment the reference count. HXFLogger pLog XFResult XFBuf_Validate HXFBuf buf Checks an XFBuf for validity. This may HXFLogger include checking that chunkBytes <= chunkSize pLog and that no guard band violations have occurred. void XFBuf_Done HXFBuf buf Returns control of an XFBuf to the HXFLogger XFBufMgr that created it. If the reference pLog count of the XFBuf is greater than one, the count is decremented and the XFBuf is not freed.

The XFBufMgr is responible for creating XFBufs and accepting them back when the XFBuf's Done method is called. What happens when Done is called depends on which XFBufMgr created the XFBuf. XFBufMgr is an abstract class. At least two concrete classes shall be derived from XFBufMgr, one for migratable and one for non-migratable buffers. The present system and method further contemplate an additional XFBufMgr that may be created to handle client owned buffers.

Table R, Table S, Table T, Table U, and Table V provide further information relative to the detailed object model for the XFBufMgr. Table R sets forth the data members. Table S indicates that XFMigratableBufMgr adds a data member, whereas XFNonMigratableBufMgr does not add any data members. In Table T, the XFBufMgr defines the indicated methods for the base class. Table U characterizes the virtual methods XFMigratableBufMgr implements, and adds two more, whereas Table V characterizes the virtual methods XFNonMigratableBufMgr implements and also adds two more. TABLE R Type Name Description unsigned type The derived class flag. This allows dynamic type checking of XFBufMgr derived types. XEngCriticalSection* cs The mutex for the buffer manager. XFList <HXFBuf> inUse The inUse list. This list tracks all the buffers issued by this buffer manager and allows garbage collection at cleanup. unsigned sizeErrors The number of times that the buffer validator method detected chunkBytes > chunkSize.

TABLE S Type Name Description HXFBuf free The head pointer to the free list. Released buffers are held here until they can be reused. unsigned beforeErrors The number of times a violation was detected on the guard band before an XFBuf. unsigned afterErrors The number of times a violation was detected on the guard band after an XFBuf.

TABLE T Return Type Name Parameters Description void virtual XFBM_Delete HXFBufMgr Pure virtual function. bufMgr See derived class for implementation. XFResult virtual HXFBufMgr Pure virtual function. XFBM_BufValidate bufMgr See derived class HXFBuf buf for implementation. HXFLogger pLog void virtual HXFBufMgr Pure virtual function. XFBM_BufDone bufMgr See derived class HXFBuf buf for implementation. HXFLogger pLog

TABLE U Return Type Name Parameters Description XFResult XFMigratableBufMgr_New HXFBufMgr Creates a new *pBufMgr XFMigratableBufMgr. void virtual XFBM_Delete HXFBufMgr Deletes all XFBufs in the free list bufMgr and deletes this instance of the XFBufMgr XFResult XFmigratableBufMgr_Alloc HXFBufMgr Allocates a migratable XFBuf (or bufMgr chooses one from the free list) XFSize size and returns it to the caller. unsigned size specifies the minimum size alignment of the new buffer. If there is an HXFBuf *pBuf existing XFBuf on the free list HXFLogger from 100 to 110% of the pLog requested size, that XFBuf will be returned. Otherwise, a new one will be allocated. alignment specifies that the allocated data block should be aligned on the requested boundary. This value must be a power of 2. pBuf receives the HXFBuf. XFResult XFMigratableBufMgr_Dup HXFBufMgr Duplicates an XFBuf. mgr A new migratable XFBuf is HXFBuf buf allocated (or selected from the HXFBuf *pBuf free list) and the contents of buf HXFLogger are copied into it. The duplicate pLog XFBuf is returned in pBuf. The new buffer will retain all existing data and flags of the original except: The MIGRATE flag will be set, and the FINISHED, NONMOVEABLE, and READONLY flags will be clear. XFResult virtual HXFBufMgr Validates that chunkBytes <= XFBM_BufValidate bufMgr chunkSize and scans for any HXFBuf buf guard band violations. HXFLogger pLog void virtual XFBM_BufDone HXFBufMgr Places the specified XFBuf onto bufMgr the free list. HXFBuf buf HXFLogger pLog

TABLE V Return Type Name Parameters Description XFResult XFNonMigratableBufMgr_New HXFBufMgr Creates a new *pBufMgr XFNonMigratableBufMgr. void virtual XFBM_Delete HXFBufMgr Deletes this instance of the bufMgr XFBufMgr XFResult XFNonMigratableBufMgr_Track HXFBufMgr Creates an XFBuf to track an bufMgr Engine allocated buffer. This HXFEng xeng buffer will be non-migratable. HXFOutput xeng refers to the XFEng that output owns the buffer being tracked. XEngChunk The Ready flag of the XFEng will *chunk be cleared. HXFBuf *pBuf output refers to the XFOutput HXFLogger that is issuing the buffer. The pLog busy flag of the XFOutput will be set. chunk is the chunk holding the description of the buffer to be tracked. pBuf receives the XFBuf handle. Note: this call will return XF_FAIL if the busy flag of the XFOutput is already set. XFResult virtual HXFBufMgr Validates that chunkBytes <= XFBM_BufValidate bufMgr chunkSize. HXFBuf buf HXFLogger pLog void virtual XFBM_BufDone HXFBufMgr Clears the busy flag of the bufMgr XFOutput that issued the buffer HXFBuf buf and signals the XFEng Ready to HXFLogger run. pLog Deletes the XFBuf instance.

The XFBufMgr class does not have any states or state transition events. Functionally, the two buffer managers will be used in slightly different ways.

If an Engine has set its migratable support flag, the Migratable buffer manager will be called before the Engine's process point in order to provide buffers for each of the Engine's outputs. When the Engine releases the buffer, it will be moved to the downstream link or discarded as appropriate. Alternatively, if an Engine does not set its migratable support flag, the Non-Migratable buffer manager may be called after the Engine's process point to provide an XFBuf wrapper for each new output buffer generated by the Engine. In the case where the buffer coming out the output was passed through from an input, the original XFBuf will be located on that input and reunited with the buffer before passing onto the XFLink.

Attention is now turned to the XFScheduler detailed design. The XFScheduler class is responsible for dividing the DAG into executable traces and then running those traces in zero or more threads depending on the client request. If the client specifies zero threads, then it must call DFlow_Process (which calls XFScheduler_Process) to execute the trace. The object model for the XFScheduler is set forth below in Table W (Members) and Table X (Methods). TABLE W Type Name Description XEngMutex * mutex The mutex that protects the thread manager. XFSchedCtrl control The control flag for XFScheduler. It can be set to: Stop, SingleStep, OneLoop. unsigned maxThreads The maximum number of scheduler threads that may be created to execute traces. The legal values are: 0: Create no threads. Only one trace will be created and it can only run when the client calls the Process method. >0: Create up to this many threads and any number of traces. Assign the traces to the threads in sequence. XF_UNLIMITED_THREADS : Create any number of threads and traces. XFList <HXFEng> * pEngines A reference to the list of Engines in the DAG. XFParamMap paramMap The Param Map is built at scheduler init time from the client-supplied parameter substitution list. It is used during the initialization of each Engine to supply actual values for any parameter macros. HXFBufMgr mBufMgr Handle to the XFBufMgr object responsible for allocating and recycling migratable buffers for the pipeline. HXFBufMgr nmBufMgr Handle to the XFBufMgr object responsible for tracking buffers allocated by individual Engines. XEngConditional * cvLoop An event flag (CV). This event occurs at the completion of each scheduling cycle to signal a waiting client thread to check for initialization or completion. XEngConditional * cvDone An event flag (CV). A thread will raise this event before exiting. This allows a client waiting to stop the scheduler to synchronize the joining of multiple threads while still allowing for a timeout. XFArray threads An array of threads. The number of threads <HXFThread> created depends on the value of maxThreads and the actual number of scheduler traces created. There shall never be more threads than traces. XEngConditional * cvReady An event flag (CV). This event signals that at least one XFEng within an inactive trace has transitioned to the Ready state. All extra threads will wake up and check to see if they are needed to run the trace. XEngCriticalSection * csTrace The critical section to protect the trace queue independently of the object mutex. unsigned nTraces The number of traces in the trace queue. HXFTrace traceHead A queue of available traces. The traces will be removed from the list by a thread wishing to execute them and returned to the list when the thread has completed its cycle. HXFTrace * traceTail The tail of the trace queue. XEngInt64 startTime The performance counter value at the last call to SetCtrl (Start). XEngInt64 elapsedTime The cumulative overhead of the scheduler so far. unsigned nThreads The multiplier for the thread-time calculation. XEngIO * anaLog The handle to the Analyzer log file. Is NULL if not logging. XEngInt64 baseTime The start time of the Analyzer log. double perfScale The performance clock scalar. XFPerfMonitor perfMon The performance monitor.

TABLE X Return Type Name Parameters Description XFResult XFScheduler_Init HXFScheduler Initializes a pre- scheduler allocated XFList XFScheduler *pEngines instance. unsigned pEngines is a maxThreads reference to the char *paramList[ ] Engines in the DAG. XFPerfCallbacks maxThreads *cbacks indicates the XCTSTR maximum number of log Base threads to create. paramList specifies the Parameter substitution list to use. This is in the XEngArgList format. cbacks references the performance callback functions. logBase is the base pathname for the performance logfiles. XFResult XFScheduler_Cleanup HXFScheduler Cleans up an scheduler XFScheduler. XFResult XFScheduler_LogErrorMsg HXFScheduler Appends another scheduler error message to an XTSTR msg XFScheduler. XFResult XFScheduler_GetErrorMsg HXFScheduler Returns the current scheduler error message from XTSTR *msg an XFScheduler. May return NULL if no message is stored. XFResult XFScheduler_SetCtrl HXFScheduler Sets the scheduler scheduler control state to the XFSchedCtrl new value specified newCtrl by the client. The XFSchedCtrl previous state is *pOldCtrl returned. unsigned If the state is going timeout from stop to run, the scheduler will create traces and start running them (in multi- thread mode). If the state is going from start to stop, the scheduler will kill all threads and delete all traces. This call will block until the state change completes or timeout occurs. XFResult XFScheduler_GetCtrl HXFScheduler Returns the current scheduler control state in pCtrl. XFSchedCtrl *pCtrl XFResult XFScheduler_PutTrace HXFScheduler Puts a trace at the tail scheduler of the trace queue. HXFTrace trace XFResult XFScheduler_TakeTrace HXFScheduler Removes a trace from scheduler the head of the trace HXFTrace queue. *pTrace XFResult XFScheduler_Process HXFScheduler Executes the next scheduler trace. XFBool singleStep XFResult XFScheduler_WaitForInit HXFScheduler Waits for the specified scheduler xeng to leave the HXFEng xeng Tolnit state or timeout unsigned occurs. timeout timeout specifies the maximum wait in milliseconds. XFResult XFScheduler_WaitForComplete HXFScheduler Waits for all Engines scheduler to move to the unsigned Complete state or any timeout Engine to move to the XFBool Error state. *pAllComplete timeout specifies the XFBool maximum wait in *pErrorDetected milliseconds. If all Engines are complete at return time, pAllComplete will be XF_TRUE, otherwise, it will be XF_FALSE. If any Engine generates an error, pErrorDetected will be XF_TRUE, otherwise it will be XF_FALSE. static XFScheduler_SetLoop HXFScheduler Called by a thread at XFResult scheduler the end of each scheduler cycle. This allows a client to efficiently wait for a change of state. static XFScheduler_SetDone HXFScheduler Called by a thread XFResult scheduler when it exits. This allows a client waiting for SetCtrl(Stop) to detect the exit and join. XFResult XFScheduler_SetReady HXFScheduler Called by a Trace scheduler when the ready status XFBool ready of an XFEng is unsigned changing. This *pnReady method provides a XFBool *pReady thread-safe clearinghouse for status changes. It will also wake up sleeping threads if the number of Ready Traces increases. void XFScheduler_AnalyzerLog HXFScheduler Creates an entry in scheduler the performance unsigned value analyzer log. const char *fmt value is the value to . . . be logged. fmt is the string to tag this log entry. It may contain printf style format specifiers which will be filled from the variable argument list . . . void XFScheduler_StateEvent HXFScheduler Called when an scheduler XFEng changes state. HXFEng xeng The event will be XFEngState relayed to the client if state it registered a monitoring callback,. void XFScheduler_DataEvent HXFScheduler Called when an scheduler XFEng receives or HXFEng xeng sends a block of data. XFBool isInput The event will be unsigned port relayed to the client if unsigned bytes it registered a unsigned tBytes monitoring callback. unsigned scanlines unsigned tScans unsigned blobs

The XFScheduler contains three internal classes, XFPerfMonitor, XFThread and XFTrace. Table Y through Table EE set forth the characteristics of these internal classes. TABLE Y XFPerfMonitor Data members Type Name Description XFPerfCallbacks cbacks The set of client callback functions. XFBool useQueue The flag to enable queuing. Events are queued and deferred in multi-threaded mode. Otherwise, they are delivered immediately and the following fields (mutex - done) are ignored. XEngMutex * mutex The mutex to protect the event queue. XEngConditional * cv The cv to synchronize the event queue. XFList queue The event queue. <HXFPEvent> XEngThread thread The event delivery thread. volatile XFBool done The flag to kill the event delivery thread.

TABLE Z XFPerfCallbacks Data Members Type Name Description HXFStateEventFunc stateFunc The client callback function for state change events. void * stateData The client data to use on state change callbacks. HXFDataEventFunc dataFunc The client callback function for data events. void * dataData The client data to use on data callbacks.

TABLE AA XFPerfMonintor Methods Return Type Name Parameters Description void XFPerfMon_DeliverEvent HXFPerfMonitor Delivers an event pm to the client. HXFPEvent event XEngThreadExitVal XFPerfMon_Dispatch XEngVoid *arg The event dispatcher thread. Only used when deferring events. void XFPerfMon_Init HXFPerfMonitor Initialize the pm performance XFPerfCallbacks monitor. *cbacks XFBool useQueue void XFPerfMon_Cleanup HXFPerfMonitor Cleanup the pm performance monitor. void XFPerfMon_Event HXFPerfMonitor Either queue or pm deliver an event HXFPEvent depending on the event current mode of operation void XFPerfMon_StateEvent HXFPerfMonitor Package a state pm event for queuing HXFEng xeng or delivery. This is XFEngState the public entry state point for a state event. void XFPerfMon_DataEvent HXFPerfMonitor Package a data pm event for queuing HXFEng xeng or delivery. This is XFBool isInput the public entry unsigned port point for a data unsigned bytes event. unsigned tBytes unsigned scanlines unsigned tScans unsigned blobs

TABLE BB XFThread Data Members Type Name Description XEngThread id The ID of the thread. This is used for joining with the thread. HXFScheduler scheduler A reference back to the parent class. XFBool done A Done flag. The thread sets this before exiting.

TABLE CC XFThread Methods Return Type Name Parameters Description XFResult XFThread_New HXFScheduler Creates a new thread instance. scheduler HXFThread *pThread void XFThread_Delete HXFThread thread Deletes a thread instance. XFResult XFThread_Start HXFThread thread Starts the thread instance. XFResult XFThread_Join HXFThread thread Joins with the thread. Will fail if the thread is not done. XFBool XFThread_IsDone HXFThread thread Indicates whether the thread is done and ready to join.

TABLE DD XFTrace Data Members Type Name Description unsigned id The id number of this Trace. HXFScheduler scheduler A reference to the parent XFScheduler. unsigned nReady The number of XFEngs in this Trace that are ready to run. unsigned currentXFEng The index of the next XFEng to be executed in this trace. XFArray Engines The array of XFEngs in this trace. <HXFEng> HXFTrace next Pointer to the next Trace in the queue.

TABLE EE XFTrace Methods Return Type Name Parameters Description XFResult XFTrace_New HXFTrace Creates a new trace instance. *pTrace void XFTrace_Delete HXFTrace trace Deletes a trace instance. XFResult XFTrace_Add HXFTrace trace Adds an XFEng to the trace. HXFEng engine XFResult XFTrace_Process HXFTrace trace Executes the trace. If the const singleStep flag is true, then only XFParamMap one XFEng will be executed. *paramMap Otherwise, the trace will execute XFBool of its XFEngs once. singleStep XFResult XFTrace_SetReady HXFTrace trace Called when the ready state of an XFBool ready XFEng is changing. This method XFBool *pReady calls its parent scheduler to perform the actual status change.

The XFScheduler has three states based on its control setting:

-   -   Stop—Stop and join all threads, delete all traces.     -   Single Step—Create traces and threads, call XFTrace_Process with         the Single Step flag set. This means that the trace can be         rescheduled to a new thread after running only one Engine. It         also means that the traces will respond to the stop condition         quickly.     -   One Loop—Create traces and threads, call XFTrace_Process with         the Single Step flag clear. This means that the trace will run         all of its Engines before being rescheduled or responding to the         stop condition.

Functionally, when DFlow is placed in the Run state, one or more scheduler traces are created to execute portions of the DAG. A number of threads are created to execute the traces from the trace pool. The lesser of the number of traces and maxthreads determines the number of threads to create.

If maxThreads is 0 or 1, all Engines are placed in a single trace. To create scheduler traces, DFlow follows these steps:

-   1) Create a new trace object. -   2) Search the Engine list for an unscheduled Source (an Engine with     zero inputs). If there are no sources but still unscheduled Engines,     then search for a ThreadBreak leading to an unscheduled Engine. Add     the selected Engine to the current trace. If no unscheduled Engines     can be located, then exit after discarding an empty trace object. -   3) Follow the links from that Engine and add each Engine to the     trace until hitting a Sink, ThreadBreak, or previously scheduled     Engine. (Note:

ThreadBreaks are only respected in the multi-thread case.) If any given Engine has multiple outputs, queue up the other outputs to be followed later on within this trace. Once all branches have been followed to completion, this trace is complete.

-   4) If this is the multi-trace mode, create a new trace object.     Otherwise, reuse the current trace. -   5) Go back to (2).

The method for executing traces differs between the client thread mode and the independent thread modes. In the client thread mode, since no threads are created, the scheduler cannot do anything independently. It must wait until the client calls DFlow_Process, which then calls XFScheduler_Process, which then calls XFTrace_Process. In the limited-thread mode, the scheduler creates up to maxThreads threads (but no more than there are traces). Those threads take the trace from the head of the list, execute it in the mode specified by the scheduler control (SingleStep or OneLoop), return it to the tail of the list, and repeat. And, in the unlimited-thread mode, the scheduler creates the same number of threads as there are traces. These threads each execute a single trace. Note that unlimited mode is simply the limited mode with no maxthreads restriction. The same thread-trace assignment model is used.

To kill traces, the control flag is set to Stop. The next time a thread returns to the scheduler to exchange its trace, it will exit. The thread that called XFScheduler_SetCtrl(Stop) will block until all threads have joined or a timeout occurs. It should be appreciated that the unusual selection of types for the head and tail pointers in the Trace queue is intended as an optimization. It eliminates all but one test from the append and remove operations.

-   lnit (New):     -   head=NULL;     -   tail=&amp;head; -   Append (PutTrace):     -   *tail=trace; tail=     -   &amp;trace-&gt;next;     -   trace-&gt;next=NULL; -   Remove (TakeTrace):     -   *pTrace=head;     -   head=head-&gt;next;     -   if (!head)         -   tail=&amp;head;     -   (*pTrace)-&gt;next=NULL;</screen>

Lastly, XFParams is a class responsible for keeping track of an XFEng's parameter set as well as translating a parameter template into an argument list compatible with an Engine lnit function. The XFParams class provides the methods for parsing the parameter template string, but the client must provide an ArgList containing the mappings between any value macro names and their actual values.

Using the XFParams class takes several steps:

-   1) Create a set of parameters or templates using XFParams_Add or by     loading an XML pipeline description. The DFlow client will do this. -   2) Create an instance of XFParamMap from an ArgList style macro     substitution list. The DFlow client must supply the ArgList when     calling DFlow_PipeRun, DFlow will convert it to an XFParamMap. -   3) Call XFParams_CreateArgv to create the final ArgList to be handed     to an Engine's lnit method.

The following tables (Table FF-Table KK) characterize the detailed object model for the XFParams (e.g., XFParams is a renamed instance of XFArray., the array holds objects of type HXFParam): TABLE FF XFParams Type Name Description XTSTR name The name of the parameter. XTSTR value The value of the parameter.

TABLE GG XFParamMap Type Name Description XTSTR name The name of the parameter. SpecType spec The data type of this parameter. E.g. Int, Double, String . . . XFArray <void *> values The array of parameter values.

TABLE HH XFArgList Type Name Description XTSTR name The name of the argument. unsigned count The array size of this argument. Positive values indicate a fixed number of parameters. 0 represents a variable length array. SpecType spec The data type of this argument. E.g. Int, Double, String . . .

TABLE II XFParams Methods Return Type Name Parameters Description XFResult XFParams_Init XFParams *pParams Initializes the XFParams instance. void XFParams_Cleanup XFParams *pParams Cleans up the XFParams instance. XFResult XFParams_Add XFParams *pParams Adds the specified XCTSTR name parameter to the XCTSTR value instance. The name . . . and value strings are duplicated internally. If the value string contains any printf style format specifiers, they are substituted with values from the variable argument list (. . .). XFResult XFParams_Copy XFParams*dstParams Duplicates the contents const XFParams of srcParams into *srcParams dstParams. The previous contents of dstParams are discarded. unsigned XFParams_GetCount const XFParams Gets the number of *pParams parameters in this instance. HXFParam XFParams_Get const XFParams Returns a reference to *pParams the parameter at unsigned index position index of the array. void XFParams_Dump const XFParams Dumps the contents of *pParams the instance to the log HXFLogger pLog at the specified level. XFLogLevel level void XFParams_DumpArgs char *args[ ] Dumps the contents of HXFLogger pLog the XEng style argList XFLogLevel level (args) to the log at the specified level. This is useful for verifying the correct resolution of all macros before they are used to initialize an Engine. XFResult XFParams_CreateArgv const XFParams Converts the *pParams parameters in pParams const XFParamsMap into the ArgList *paramMap referenced by argList. const XEngFuncDesc Any macros in the *desc parameters are char *argList[ ] substituted using the XEngSmartObject mappings in **garbage paramMap. HXFLogger pLog The conversion process may generate some allocated garbage that must be freed after the argList is consumed by the Engine's Init function.

TABLE JJ XFParamMap Methods Return Type Name Parameters Description XFResult XFParamMap_Init XFParamMap Initializes the XFParamMap *paramMap instance. char The value mappings contained *paramList[ ] in paramList are converted into an XFParamsMap. void XFParamMap_Cleanup XFParamMap Cleans up the XFParamMap *paramMap and frees any allocated storage.

TABLE KK XFArgList Methods Return Type Name Parameters Description XFResult XFArgList_Init XFArgList Initializes the XFArgList *pArgList instance. void XFArgList_Cleanup XFArgList Cleans up the XFArgList *pArgList and frees all allocated storage. XFResult XFArgList_AddArgs XFArgList Parses the parameter set in *pArgList pParams to locate any const macros. The types of the XFParams macros are derived from *pParams desc and the resulting const formal argument is merged XEngFuncDesc with pArgList. *desc HXFLogger pLog XFResult XFArgList_ExportArgDesc const XFArgList Exports the current *pArgList contents of pArgList as an char ***argDesc array of strings. This array may be stored directly in the args field of an XEngFuncDesc.

The XFParams class does not have any states or state transition events. However, functionally XFParams provides two methods of parsing a parameter template set. CreateArgv takes a parameter set as an input and converts it to an Engine style ArgList. It also detects macros in the parameter set and inserts appropriate references to the actual values when building the ArgList. GetArgDesc takes a parameter set as an input and locates all the macros. The compiled set of macros is then exportable as an argument descriptor list.

It may also be noted that, from a data structure perspective, the disclosed method and system contemplate that the DFlow DAG may be serialized to an XML file. Further contemplated herein is the addition of a DAG “Expert”. For example, a callback system may be implemented where registered “Experts” will be given the opportunity to modify a DAG prior to it executing. Examples of possible “Experts” include: an auto-formatting module that will insert the correct engines to account for required image formats to other engines; and an auto-thread breaking module that will insert thread breaks such that the DAG executes more efficiently on the given platform (especially multi-CPU/core systems).

It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

1. A method for processing image data, comprising: defining a multi-trace directed acyclic graph, including breaking a directed acyclic graph for processing image data into a plurality of traces, wherein each trace is a fragment of the directed acyclic graph; and executing the multi-trace directed acyclic graph wherein each trace is executed in a separate thread.
 2. The method of claim 1, wherein executing the multi-trace directed acyclic graph utilizes a plurality of processors in a multi-processor system.
 3. The method of claim 2, wherein the plurality of processors are spread across networks on multiple computers.
 4. The method of claim 1, wherein defining a multi-trace directed acyclic graph comprises: automatically creating a new trace for each source found; and growing each new trace by following links out from each source.
 5. The method of claim 1, wherein the image data includes a plurality of chunks of image data and where said chunks of image data comprise an integral number of image scanlines.
 6. The method of claim 1, wherein said directed acyclic graph includes at least one instance of an engine.
 7. The method of claim 5, further including serializing the directed acyclic graph to an extensible markup language file.
 8. The method of claim 1, further including a callback system wherein a directed acyclic graph is modified prior to its execution.
 9. A system for processing image data in a networked computing environment, comprising: an image data source; a host system, connected to said image data source via the network, wherein said host system includes an image processing pipeline, said pipeline operating on chunks of image data from said source; and memory for storing said chunks of image data during and upon completion of the data by the pipeline.
 10. The system of claim 9, wherein said pipeline comprises a dataflow scheduler, said dataflow scheduler interfacing with at least one node within the image-processing pipeline.
 11. The system of claim 10, wherein the dataflow scheduler describes, runs, and controls the input of image data to said image-processing pipeline.
 12. The system of claim 10, wherein said pipeline includes a directed acyclic graph, said system further comprising: a directed acyclic graph manager function; and a buffer manager function.
 13. The system of claim 10 wherein said pipeline operates within an engine layer, and wherein said dataflow scheduler controls the operation of at least one node in said engine layer.
 14. The system of claim 12, wherein the host system includes a plurality of processors executing the directed acyclic graph and where the plurality of processors are spread across at least one network.
 15. An image processing pipeline, comprising: a client layer; a dataflow layer, said dataflow layer including at least one interface and service to describe, run, and feed the image-processing pipeline; and an engine layer, wherein said dataflow layer controls the operation of at least one node in said engine layer.
 16. The image processing pipeline of claim 15, wherein said dataflow layer further comprises: a directed acyclic graph manager, allowing a client to describe nodes and edges of a directed acyclic graph, wherein the nodes represent engines and the edges represent the data flow links between them; a buffer manager for handling a plurality of chunk buffers; and a scheduler for dividing the directed acyclic graph into executable traces, and creating threads to run the executable traces.
 17. The image processing pipeline of claim 16, wherein the chunk buffers are selected from the group consisting of: migratable, non-migratable, and client-owned chunks of data.
 18. The image processing pipeline of claim 15, wherein the dataflow layer further comprises: an editor to describe an image processing pipeline; memory to save a description of an image processing pipeline; a memory interface to load a previously saved description; and a processor interface to run the currently loaded description, and extract performance statistics.
 19. The image processing pipeline of claim 18, wherein the client layer may run the pipeline using a method including feeding an input image to the pipeline as a chunked stream and retrieving chunks interactively.
 20. The image processing pipeline of claim 15 further including a plurality of processors in a multi-processor system, said processors executing the multi-trace directed acyclic graph. 